1. Field of the Invention
This invention relates to throttled internal combustion engines which utilize both the four-stroke combustion cycle and stratification of the intake charge. The engine may have either a piston or a rotary configuration, but its strata of varying mixture strength result from establishing distinctly different air-fuel or dilution ratios in the mixture inducted separately through two or more engine intake passages.
This invention also relates to methods for regulating the brake torque output of the foregoing type of stratified charge engine.
2. Description of the Prior Art
Although employing two or more intake valves for each cylinder of a piston engine is a long known way of improving engine breathing, establishing charge stratification in such engines via barrel swirl is a much more recent discovery. U.S. Pat. No. 5,050,557 (Ishida et al.), U.S. Pat. No. 5,273,973 (Oda), U.S. Pat. No. 5,273,974 (Isomoto et al.) and U.S. Pat. No. 5,295,464 (Ando et al.) all disclose barrel-stratified piston engines. At the same time, combustion chambers with three or more poppet valves usually employ the pentroof configuration, which leaves little room conveniently available for turbulence enhancing squish area. As a result, barrel swirl and a central spark plug location must be relied on to such an extent that other disadvantages arise. For example, the bulk flow of a very high barrel swirl ratio can easily blow the ionization path from between a spark plug's electrodes to such a degree that the path is broken. As another example, using a central spark plug location precludes utilizing the particular type of barrel swirl that is most pronounced and most easily maintained during the compression stroke. In the case of the Wankel rotary engine, barrel stratification does have its analogy, but the prior art makes no mention of this new type of stratification in rotary engines.
Of the prior art just mentioned, only Oda '973 considers employing variable stratification in combination with the engine throttle valve in an overall scheme for regulating engine brake torque output. Using throttling exclusively at lower brake mean effective pressure (BMEP), and variable stratification exclusively at higher BMEP, produces the maximum efficiency gain, but the prior art discloses a blended rather than a segregated combination of these two types of BMEP regulation.